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The finite element method has employed to simulate the laser thermal cracking process for brittle materials. The varieties of temperature and thermal stress distributions around the crack tip were studied. The effect of cracking parameters, i.e. laser power, focus moving speed, plate thickness, crack length, cooling effect¡K etc., on the crack propagation has also investigated. The stress intensity factor around crack tip is considered as the key parameter to dominate the crack propagation. The thermal-plastic-elastic finite element model was employed to simulate the temperature and stress distributions. The strain energy release rate and stress intensity factor solved from virtual crack closure technique and displacement extrapolation method are employed to illustrate the crack state in this study. Five crack length models were used to show the stress intensity factor variations around the crack tip. Numerical results indicate that the head flux on the surface, substrate thickness and adopting cooling sources may affect the crack propagation, crack delay significantly. The results in this study also demonstrate the feasibility of employing finite element method in the exploring crack propagation mechanism in laser thermal cracking process.

Nb3Al base alloys were produced in ingot or ribbon form using cold hearth non-consumable tungsten arc melting and chill block casting by melt overflow on a Mo wheel. The following alloys were studied: Nb-25Al, Nb-18Al, Nb-18Al-xMo (x=20,30,40) and Nb-18Al-9Cr-5Ti (at%). Low levels of interstitials (< 200 wppm O2, < 10 wppm H2) were achieved in all alloys. The effects of alloy chemistry and method of solidification processing on phase selection, solidification microstructures and solid state phase transformations were studied. Room temperature microhardness and hardness of the alloys were evaluated. The A2 structure (disordered beta Nbss) transformed to the B2 structure (ordered beta Nbss) by solid state transformation in the Nb-18Al and Nb-18Al-xMo (x=20,30,40) alloys. The experimental results showed that Al promoted A2&rarr;B2 ordering in Nb rich binary Nb-Al alloys and confirmed the predictions of thermodynamic modelling of A2&rarr;B2 ordering in the Nb-Al system. Mo addition inhibited the A2&rarr;B2 ordering whereas Cr+Ti additions favoured ordering. Formation of an o-phase was observed for the first time in the binary Nb-Al system after prolonged annealing of the Nb-18Al ribbons (973 K / 500 h). It is suggested that the o-phase forms as a transition phase in the transformation B2&rarr;o&rarr;Al5. While o-phase formation has been reported in alloys of the Nb-Al-Ti system, it is shown that Mo addition does not favour the o-phase in Nb-18Al-xMo alloys (x=20,30,40). Formation of o diffuse in the beta phase supports a previous hypothesis that addition of Al to transition metal elements such as Nb,Mo,V can enhance formation of the o phase in the beta phase. Mo addition in the Nb-Al solid solution increases the electron density of A2 or B2 phases and consequently the deviation | Delta | of the o diffuse from crystalline o. A new ternary o type phase, o*, was formed as a transition phase in the B2?Al5 transformation in heat treated Nb-18Al-xMo (x=20,30,40) alloys (973 K / 500 h). The orientation relationship of o* is [111]B2//[0001]o* and (110)B2//(0110)o* and the lattice parameters are ao* = 61/2aB2 and = c o* = 31/2aB2. Rapid solidification refined the alloy microstructures by two orders of magnitude. The room temperature solid solubility of Al in Nb was extended from 6 at% to 25 at% Al. In Nb-18Al-9Cr-5Ti up to 5at%Ti+8.4at%Cr were retained in solid solution. Suppression of Nb3Al and Nb2Al formation was achieved in the ribbons of Nb-25Al. Nb3Al formation was suppressed in the ribbons of Nb-18Al, Nb-18Al- xMo (x=20,30,40) and Nb-18Al-9Cr-5Ti. The A2-*B2 ordering was suppressed in the ribbons of all Nb-18Al-xMo alloys and in the as cast ingots of Nb-18Al-40Mo. Aluminium additions in Nbss increased its microhardness by 16.6 kgmm-2/at%Al and Mo addition hardened the Nbss (16.1at%Al) by 4.2 kgmm-2/at%Mo. Regarding the oxidation behaviour, the Nb-18Al-20Mo and Nb-18Al-9Cr-5Ti alloys exhibited lower weight gain rates as compared to Nb3Al. No protective scale was formed on any of the alloys studied in this work.

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京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19394号 / 理博第4125号 / 新制||理||1593(附属図書館) / 32419 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 平島 崇男, 教授 土`山 明, 准教授 河上 哲生 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

North-eastern part of the Bohemian Massif is characterised by many NW-SE striking faults. The Sudetic Marginal Fault Zone (SMFZ) and Hronov - Poříčí Fault Zone (HPFZ) represent the major seismoactive dislocations in this area. Field structural investigations, including fault-slip data collection were carried out on a number of natural outcrops and quarries with the aim of establishing a robust and field-constrained model for the local brittle structural evolution of the studied areas. Almost 5000 faults and fractures have been measured and studied in 116 localities. Two principle sets of faults within the SMFZ are oriented in the N-S and W-E directions. The faults are mainly dipping under 80-90ř. The lineations found on the fault planes are mainly trending to the SW and W. The kinematic frequent analysis was performed due to the distribution of the fault types in the orientations. The faults were divided into the different tectonic phases based on their origin or reactivation and their relative age using the calculation of paleostress analysis. The paleostress analysis of the fault-slip data within the SMFZ resulted identification of six tectonic phases from the youngest to the oldest: strike-slip regime with maximum compression σ1 in the NNW-SSE direction, compressional regime with σ1 in the...

The dissertation focuses on the analysis, through combined analytical and numerical techniques, of the partial differential equations arising from a new approach to modeling brittle fracture, based on extension of continuum mechanics to the nanoscale. The main part of this work deals with the analysis of several fracture models. Integral transform methods are used to reduce the problem to a Cauchy singular, linear integro-differential equation. It is shown that ascribing constant surface tension to the fracture surfaces and using the appropriate crack surface boundary condition, given by the jump momentum balance, leads to a sharp crack opening profile at the crack tip, in contrast to the classical theory of brittle fracture. However, such a model still predicts singular crack tip stress. For this reason a modified model is studied, where the surface excess property is responsive to the curvature of the fracture surfaces. It is shown that curvature-dependent surface tension, together with boundary conditions in the form of the jump momentum balance, leads to bounded stresses and a cusp-like opening profile at the crack tip. Further, an alternative approach, based on asymptotic analysis, which is suitable to apply in cases when the model includes a mutual body force correction term, is considered. The nonlinear nonlocal problem, resulting from the proposed model, is simplified which allows us to approximate the crack opening profile and derive asymptotic forms for the cleavage stress in a neighborhood of the crack tip. Finally, two possible fracture criteria, in the context of the new theory, are discussed. The first one is an energy based fracture criterion. Classically the energy release rate arises due to singular fields, whereas in the case of the modeling approach adopted here, a notion analogous to the energy release rate arises through a different mechanism, associated to the rate of working of the surface excess properties at the crack tip. Due to the fact that the proposed modeling approach allows us to fully resolve the stress in a neighborhood of the crack tip, without the customary singularity, a second fracture criterion, based on crack tip stress, is possible.

One of the most fundamental and critical functions of embryological development is the control and regulation of differential genes and gene networks. The study of the gene networks involved in development is a mechanism for understanding the developmental process at its most basic level. An evolutionary change in a morphological feature or features must depend on a reorganization or co-option of one or more developmental gene regulatory network just as retention of an ancestral morphological trait must rely on retention of a common gene regulatory network. Studying two closely related classes in the same phylum with the same essential morphological feature yet with unique developmental characteristics provides insight into the evolution of these evolutionarily resolute gene regulatory networks. We have developed a new model system using brittle stars to further these studies. In this investigation I have identified key genes of the gene regulatory network (GRN) found in embryonic endo-mesoderm development in the sea urchin, responsible for embryonic skeletogenesis, and compared these key genes with homologues in the brittle star. From the examination of two closely related gene regulatory networks found in two related classes of Echinoderms insight can be gained into the foundation of morphological change over time.

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